Most commercially available fluorinated surfactants are produced through electrochemical fluorination or telomerization. Electrochemical fluorination utilizes anhydrous hydrofluoric acid as the fluorine source. However, industrially produced hydrofluoric acid contains impurities; which requires use of further complicated processes to remove these impurities.
Telomerization processes use tetrafluoroethylene as the starting material. However, tetrafluoroethylene is a hazardous and expensive intermediate with limited availability. The telomerization products contain a mixture of homologs which contain a distribution of different carbon chain lengths, typically containing chain lengths of from about 4 to about 20 carbons. Therefore, in order to produce fluorinated surfactants which contain a fluorinated carbon chain of fixed length, and not a mixture of various lengths, some sequential separation of telomerization products is required, as described by Erik Kissa in “Fluorinated Surfactants, Synthesis-Properties-Applications”. For example, U.S. Pat. No. 6,537,662 discloses a fluorochemical which may be incorporated into a soil-resistant spin finish composition as one of the optional additives. The fluorochemical additive includes fluorochemical polyoxyethylene diamides.
There is disadvantage of using such fluorinated surfactants containing longer perfluoroalkyl chains. For example, Koji Honda et al., in “Molecular Aggregation Structure and Surface Properties of Poly(fluoroalkylacrylate) Thin Films” Macromolecules (2005), 38(13), 5699-5705, teach that the orientation of the perfluoroalkyl chains of at least 8 carbons is maintained in a parallel configuration, while for such perfluoroalkyl chains containing less than 6 carbons, reorientation occurs. This reorientation decreases performance effects for altering surface behaviors. Further, the price of fluorinated surfactant is primarily determined by the amount of fluorine incorporated in compound. Therefore, it is desirable to obtain fluorinated surfactants which can be prepared from fluorinated chemicals other than telomers. It is further desired to obtain fluorinated surfactants which contain shorter fluorinated chains or fluorinated groups and still provide essentially the same or even superior performance for altering surface behaviors. Especially desirable is lowering surface tension, and providing to liquids low surface tension, low interfacial surface tension values, and low critical micelle concentrations. The present invention provides such fluorinated surfactants.